As one of the techniques in inserting a syringe needle into a blood vessel in intravenous injection and blood collection, medical doctors and nurses estimate the location of a blood vessel by observing and/or touching skin and insert a needle. A large portion of this technique, relies on the person's experience and intuition. Thus, the goal of needle insertion is not always achieved certainly by the first insertion.
A cause of such uncertainty in the technique of inserting a needle into a vein is that some blood vessels inside a body cannot be seen directly, and therefore it is difficult to figure out where they are located, how they extend, what kind of shape they have, and so forth. In addition, another cause is that apart of a syringe needle having been inserted into a body cannot be seen with the naked eyes, and therefore the true positional relationship between a blood vessel and the needle cannot be recognized.
To solve these problems, Patent Document 1 discloses an invention that visualizes the state of a blood vessel by use of infrared rays. In addition, Patent Document 2 discloses a method of allowing the state of a blood vessel to be seen with the naked eyes by use of light having a wavelength of 700 to 800 nm. Moreover, Patent Document 3 discloses a method in which a hotspot obtained by an infrared ray detector is assumed as a blood vessel and the location of the hotspot is indicated with pigment or a point light source. Further, Patent Document 4 discloses an apparatus with which the location of the tip of a syringe needle inside a body is estimated based on the shape of the syringe and the estimated location of the tip of the needle is synthesized with an image of a blood vessel and displayed. Furthermore, Patent Document 5 discloses an apparatus with which the location of a vein is detected by use of an ultrasonic wave and a syringe needle is moved forward in the direction of a reflected wave.